I had a bad experience at a meeting after a red eye with zopiclone. It worked fine for sleeping, but the next afternoon - when asked a question in the board room, my mind went completely blank in one of those "I must be the dummest people ever" moments. It was actually quite concerning.

Since then I've been switched to a very short acting (2-4 hrs) prescription hypnotic which is safe and hardly used any more - chloral hydrate. Seems to work well for YVR-YYZ flights etc.